The present invention relates to a method for unloading a solid substance having a high degree of water from a cargo hold of a bulk carrier such as a ship or barge. The method utilizes a pump seated on a float that is freely movable on a layer of liquid that is formed above at least portions of the solid substance due to its high degree of water content. The invention also relates to a method of loading a solid substance having a high degree of water content into a cargo hold of a bulk carrier, as well as to a float having a pump station seated thereon, for use in the loading and unloading of a solid substance having a high degree of water content into and from a cargo hold of a bulk carrier.
In a continuously increasing extent, a need is present to reclaim land areas in order to make active use of the land. For that purpose, large volumes of substance, like sand, is transported from one land area to another by use of barges. One example is reclamation of land areas previously being sea areas. This is i.a. true for the new airport near Osaka in Japan. Another example is reclamation of land for expansion of city areas like in Singapore. Yet an example is desert sand being transported by barges from Sahara to the Canary Islands for developing beaches or establishing sand beaches on locations previously not having such.
In order to increase the productivity for these development projects, the thought of exploiting available bulk carriers as transportation means has been introduced. The present concept does introduce an effective way to load and unload a ship. Especially seabed substance, and in particular, though not exclusively, sand is exploited for these projects.
According to one embodiment of the present invention, a solid substance having a high degree of water content, is unloaded from a cargo hold of a bulk carrier by a pump seated on a float that is freely movable over a layer of liquid that is formed over the solid substance due to the high degree of water content of the solid substance.
In accordance with the principles of the invention, solid substance and water are pumped out of the cargo hold in a predetermined volumetric ratio and simultaneously, water is fed into the cargo hold at a volumetric rate that is substantially the same as the water volume being pumped out with the solid substance. Preferably, the volumetric ratio of water and solid substance being pumped out of the cargo hold is between 70:30 and 60:40.
The pump suction is suitably displaceable outwardly and inwardly in the vertical direction in respect of the float, in order to adjust and adapt itself according to the optimum ratio of the solid substance and the water in the discharged mixture.
Further, a method for loading as stated in the preamble of this specification is provided, which is distinguished in that during loading, the water is pumped outboard again from the cargo hold by the pump on the float at substantially the same volumetric rate as the water arriving inboard, and the water layer is kept deeper than during unloading in order to let the solid matters settle and as little as possible of the solid matters are allowed to pass outboard again with the water being pumped outboard.
Still further, a float as stated in the preamble of this specification is provided, which is distinguished in that at least the suction of the pump station can to be elevated or lowered in respect of the float. As an alternative, the entire pump station can be elevated or lowered in respect of the float. The float can have a stationary guiding column to which a beam, that can be elevated or lowered, carrying the entire pump station, is provided. The pump station can include a motor, which is in driving connection to a pump. Further, the motor can be connected to the pump via a transmission and a support. The pump can per se be a standard mud or sand pump.
The entire float, the accompanying pump station, pipelines and hoses are an easy task to assemble on existing bulk carriers. The equipment can be designed to the actual dimension of the ship. The installation proper does not require permanent modifications or interventions in the hull of the ship. Normally one of the for-and-aft sides of the ship will be dedicated for loading and the opposite for-and-aft side for unloading.